全文获取类型
收费全文 | 591篇 |
免费 | 16篇 |
国内免费 | 4篇 |
专业分类
化学 | 432篇 |
晶体学 | 15篇 |
力学 | 7篇 |
数学 | 56篇 |
物理学 | 101篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 12篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 36篇 |
2012年 | 27篇 |
2011年 | 26篇 |
2010年 | 17篇 |
2009年 | 12篇 |
2008年 | 38篇 |
2007年 | 40篇 |
2006年 | 39篇 |
2005年 | 33篇 |
2004年 | 32篇 |
2003年 | 40篇 |
2002年 | 29篇 |
2001年 | 18篇 |
2000年 | 16篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 8篇 |
1976年 | 3篇 |
1974年 | 6篇 |
1973年 | 2篇 |
1968年 | 2篇 |
1966年 | 2篇 |
1961年 | 1篇 |
排序方式: 共有611条查询结果,搜索用时 15 毫秒
61.
Junya Kobayashi Motoo Kinoshita Jun-ichi Kita Katsumi Yoshino 《International Journal of Infrared and Millimeter Waves》1996,17(7):1149-1163
Experimental infrared modulator elements have been fabricated utilizing the transient light scattering effect of ferroelectric liquid crystal with asymmetric waveform voltage drive. The new elements perform 80% modulation degrees at the 632.8nm. We have also achieved 30% modulation degrees in the 4 to 5µ m region where the strongest CO2 absorption bands exist. A new type of analyzer which monitors ambient air quality has been developed. This analyzer uses non-dispersive infrared absorption method and composes of a double-beam, a single detector and a pair of liquid crystal light modulator as the IR chopper. The detection has achieved 10ppm noise equivalent concentration. 相似文献
62.
63.
Tomomi Kawamura 《Topology》2007,46(1):29-38
Rasmussen introduced a knot invariant based on Khovanov homology theory, and showed that this invariant estimates the four-genus of knots. We compare his result with the sharper slice-Bennequin inequality for knots. Then we obtain a similar estimate of the Rasmussen invariant for this inequality. 相似文献
64.
Takashi Yoshino 《Israel Journal of Mathematics》1991,75(2-3):273-275
In 1982, S. Friedland proved that a bounded linear operator A on a Hilbert space is normal if and only if (αI + A + A*)2 ≧ AA* − A*A ≧ −(αI + A + A*)2 for all real α. And he conjectured the inequality (αI + A + A*)2 ≧ AA* − A*A for all real α will imply that A*A − AA* ≧ 0, i.e., A is hyponormal. But his conjecture is incorrect. In this
note I’ll give a counter-example for his conjecture. 相似文献
65.
Uniform rotation of smectic layers of a ferroelectric liquid crystal in an asymmetric electric field
An asymmetric ac electric field with amplitudeE=10 V/μm gives rise to a matched rotation of the normal to the smectic layers, while a sinusoidal fieldE=1 V/μm is used to study the rotation in the method of modulation total internal reflection ellipsometry, which makes it possible to probe the region of a ferroelectric liquid crystal (FLC) next to the electrode (h≈0.7 μm). It is shown that the angle of rotation of the normal to the smectic layers near the surface of the electrode varies reversibly as a function of the polarity and number of electric pulses applied, just as in the interior region. The characteristic dynamic properties of thin layers of nematic liquid crystals, such as an anomalously long relaxation time and a high-frequency relaxation process, are observed in thin FLC layers. 相似文献
66.
Abe T Matsumoto M Hashimoto S 《The Journal of the Acoustical Society of America》2007,122(5):2697-2705
A time-domain epsilon-filter (TD epsilon-filter) is a nonlinear filter that can reduce noise while preserving a signal that varies drastically, such as a speech signal. Although the filter design is simple, it can effectively reduce noise. It is applicable not only to stationary noise but also to nonstationary noise. It cannot, however, be applied when the amplitude of noise is relatively large. This paper introduces an advanced method for noise reduction that applies an epsilon-filter to complex spectra, namely a time-frequency epsilon-filter (TF epsilon-filter). This paper also introduces noise reduction combining a TD epsilon-filter and a TF epsilon-filter. An advanced method called a variable time-frequency epsilon-filter is also proposed. First, the algorithm of the TD epsilon-filter is explained to clarify the problem. Then, the algorithms of the proposed methods are explained. By utilizing an epsilon-filter in the frequency domain, the proposed method can reduce not only noise that has a relatively small amplitude but also noise that has a relatively large amplitude. Experimental results are also given to demonstrate the performance of the proposed methods in comparison to the results of some conventional methods. 相似文献
67.
Various N,N-dimethyl amides, N-methoxy-N-methyl amides, and isopropyl esters were smoothly transformed into the corresponding nitriles in good to moderate yields by the treatment with diisobutylaluminium hydride, followed by treatment with molecular iodine in aq ammonia. The present reactions are novel one-pot and practical methods for the transformation of N,N-disubstituted amides and isopropyl esters into nitriles, through the formation of hemiaminal O-AlBu2 and hemiacetal O-AlBu2, respectively. 相似文献
68.
69.
It has been experimentally shown that an O(-c)-polar ZnO surface is more stable than a Zn(+c)-polar surface in H(2) ambient. We applied first-principles calculations to investigating the polarity dependence on the stability at the electronic level. The calculations revealed that the -c surface terminated with H atom was stable maintaining a wurtzite structure, whereas the +c surface was unstable due to the change of coordination numbers of Zn at the topmost surface from four (wurtzite) to six (rock salt). This causes the generation of O(2) molecules, resulting in instability at the +c surface. 相似文献
70.
Itoh A Saitoh T Tani K Uchigaki M Sugimoto Y Yamada J Nakajima H Ohshiro H Sun S Tanahashi T 《Chemical & pharmaceutical bulletin》2011,59(8):947-951
From the embryos of the seeds of Nelumbo nucifera, three bisbenzylisoquinoline alkaloids, nelumboferine and nelumborines A and B, were isolated along with four known compounds, neferine, liensinine, isoliensinine and anisic acid. The structures of the new alkaloids were determined mainly by spectroscopic methods. 相似文献